Pain and neural transmission Flashcards
Name some somatosensory receptors in the skin
- Meissner corpuscle
- Pacinian corpuscle
- Ruffini’s corpuscles
- Merkel’s disks
- Free nerve endings
Where are sensory receptors detecting light touch located?
Closer to the surface
Which sensory receptor detect pain?
Free nerve endings: Nociceptors
Where are free nerve endings found?
In the top layer of the dermis and the epidermis
Where are Nociceptors found?
In the periphery as simple free nerve endings.
How do Nociceptors terminate in the dermis?
Peripheral nerve fibre branches & terminates as naked, unmyelinated endings in dermis.
What does naked mean when describing nerves?
Means the nerves are unmyelinated
Can a pain response be initiated only by the stimulation of a pain receptor?
No you need to induce other things and release other substances
What does tissue damage and inflammation trigger?
release of substances e.g prostaglandins, bradykinin and histamine that can sensitize peripheral nociceptors and induce hyperalgesia.
What can chemical mediators like prostaglandins, bradykinin and histamine do?
They can can sensitize peripheral nociceptors and induce hyperalgesia.
What is hyperalgesia
Induces more pain (ie increasing the pain response)
What do we need to initiate hyperalgesia?
Need free nerve ending and the relapse of chemical mediators at the site of damage
Why do we need an increased pain response?
It is like positive feedback as the pain will stop us from harming the area further
What occurs in free nerve endings?
Transduction of painful stimuli
Where does the Transduction of painful stimuli occur?
Occurs in the free nerve endings of unmyelinated ‘C’ fibres and thinly myelinated ‘Ad’ fibres.
What are the 2 types of pain fibres?
Some nociceptors only respond to ONE modality
Most nociceptors are POLYMODAL and respond to mechanical thermal and chemical stimuli
What are some modalities nociceptors can respond to?
1, Mechanical response to strong pressure
- Thermal response to burins heat or extreme cold
- Chemical response to histamine or other chemicals
Where are Thermoreceptors found?
Deep in the epidermis
What do Thermoreceptors respond to?
Warm or cold stimuli
What type of receptors do Thermoreceptors have?
Bare nerve endings
Where are nociceptors found?
In the epidermis
What type of receptors do nociceptors have?
Bare nerve endings
Describe how are sensory transduction occurs
- Stimulus deforms or changes the nerve ending.
- This Alters the membrane permeability of the receptor membrane.
- This then Produces a receptor (generator) potential.
- This Triggers an action potential which travels along the axon to the CNS.
Name the cells and fibres involved in a sensory transaction
- Receptor endings
- Pain and temperature afferent fibres
- Mechanosensory afferent fibres
- Dorsal rot ganglion
- Spinal cord
How can we see how the nociceptors are distributed in the skin?
By using a technique called microneurography
What is microneurography?
Recording Transcutaneous nerves in humans
What are the 3 steps involved in microneurography?
- Thermal stimuli applied to receptive field of cutaneous thermoreceptor and nociceptor
- Record afferent firing in response to incremental temperatures
- Graph plotting afferent firing frequency versus temperature
What type of fibres make up Thermoreceptors sensitive to high temperatures?
C fibres
What type of fibres make up Thermoreceptors sensitive to low temperatures?
A Delta fibres
What type of fibres make up Nociception sensitive to sharp pain?
A Delta fibres
What type of fibres make up Nociception sensitive to burning pain?
C fibres
Which fibres are found in the tooth pulp?
Mostly A delta and c fibres but not all of them are pain fibres
Generally what do nerve fibres with larger diameters tend to be associated with?
Large diameters mean the nerve impulse with be more rapidly conducted
This is associated with low threshold mechanoreceptors.
Generally what do nerve fibres with smaller diameters tend to be associated with?
Small diameter means the nerve impulses will conduct slower
This is associated with nociceptors and thermoreceptors.
What is induction velocity positively correlated with?
Axon diametre
Name the sensory receptors from largest to smallest diametre
- Proprioceptors of skeletal muscles
- Mechanoreceptors of skin
- Pain and temperature receptors
- Itch receptors
Describe first pain
- Fast A-delta fibres
- Sharp or prickling
- Easily localised
- Occurs rapidly
- Short duration
- Mechanical or thermal nociceptors